The presently commercially-practiced processes for the manufacture of ethylene oxide from ethylene involve the epoxidation of ethylene over a silver containing catalyst in the presence of an oxygen-containing gas and vaporous organochloride inhibitor at elevated temperature and pressures. Considerable effort has been devoted by researchers in the field to enhance the efficiency of consumed ethylene to the sought ethylene oxide product. The primary thrust of these efforts has been toward the addition of catalyst performance-enhancing promoters to the catalysts.
U.S. Pat. No. 4,908,343 and a related United States patent application Ser. No. 251,814, filed Oct. 3, 1988, disclose the use of cations containing at least cesium cation and oxyanions of an element other than oxygen therein being selected from groups 3b through 7b, inclusive, of the Periodic Table of the Elements (as published by The Chemical Rubber Company, Cleveland, Ohio, in CRC Handbook of Chemistry and Physics, 46th Edition, inside back cover, all references herein to the Periodic Table of the Elements will be to the version set forth therein). These oxyanions, while appearing to provide enhanced efficiency of conversion of ethylene to ethylene oxide, generally also promote the burning of ethylene oxide, once formed, to undesirable combustion products, particularly at the higher ethylene oxide production concentrations which are commercially atttractive. Accordingly, catalysts are sought which attenuate ethylene oxide burning in the presence of these types of oxyanions.
U.S. Pat. No. 4,908,343 discloses impregnated silver catalysts on a support in which there is provided a mixture of at least one cesium salt and one or more alkali metal and alkaline earth metal salts. The anions of the cesium salts comprise oxyanions of elements other than the oxygen therein having atomic numbers of at least 15 to 83 and being from groups 3b through 7b, inclusive, of the Periodic Table, and the salts of the alkali metals and/or alkaline earth metals comprise at least one of halide of atomic number of 9 to 53, inclusive, and oxyanions of elements other than oxygen therein having an atomic number of either (i) 7 or (ii) 15 to 83, inclusive, and selected from the groups 3a to 7a, inclusive, and 3b to 7b, inclusive, of the Periodic Table. Often the catalyst contains at least one anion other than an oxyanion of an element of groups 3b to 7b. At column 15, lines 62 et seq., the patent relates:
"The types of oxyanions suitable as counterions for the alkali and alkaline earth metals provided in the catalysts of this invention comprise by way of example only, sulfate SO.sub.4 .sup.-2, phosphates e.g., PO.sub.4.sup.-3, manganates, e.g., MnO.sub.4 .sup.-2, titanates, e.g., TiO.sub.3 .sup.-2, tantalates, e.g., Ta.sub.2 O.sub.6 .sup.-2, molybdates, e.g., MoO.sub.4 .sup.-2, vanadates, e.g., V.sub.2 O.sub.4 .sup.-2, chromates, e.g., CrO.sub.4 .sup.-2, zirconates, e.g, ZrO.sub.3 .sup.-2, polyphosphates, nitrates, chlorates, bromates, tungstates, thiosulfates, cerates, and the like. The halide ions include fluoride, chloride, bromide and iodide. PA0 "These investigations have led to the discovery that the use of the aforesaid specified halogen elements . . . previously believed to have a poisonous action, in combination with sodium and cesium unexpectedly gives a catalyst having greatly increased performance." PA0 "It is of little importance with which radical (anion) cesium and/or rubidium is associated. They can be inorganic or organic radicals, especially in the form of salts, hydroxides, alcoholates and phenolates. However, this radical should not consist of substances which, in particular after treatment with the gaseous reaction mixture for the preparation of ethylene oxide at 230.degree. to 270.degree. C., act as a so-called `catalyst poison.` Radicals (anions) suitable for the process can be, for example: sulfate, nitrite, chloride, bromide, fluoride, chlorate, bromate, cyanate, silicate, oxalate, malonate, succinate, butyrate, laurate, stearate, benzoate and phenolate." PA0 "Formates, acetates, carbonates, bicarbonates, nitrates, hydroxides or alcoholates of aliphatic alcohols with 1 to 3 C atoms are preferably employed." PA0 "Suitable alkali metal promoter compounds include all those soluble in particular the solvent or solubilizing agent employed. Accordingly, inorganic and organic compounds of alkali metals, such as, nitrates, halides, hydroxides, sulfates and carboxylates may be used." PA0 "There are known excellent methods of applying the promoters coincidentally with the silver on the carrier. Suitable alkali metal salts are generally those which are soluble in the silver-impregnating liquid phase. Besides the above-mentioned compounds may be mentioned the nitrites; the halides, such as fluorides, chlorides, iodides, bromides; oxyhalides; bicarbonates; borates; sulfates; sulfites; bisulfates; acetates; tartrates; lactates; and isopropoxides, etc."
Examples 30, 33, 36, 37, 38 and 42 of U.S. Pat. No. 4,908,343 illustrate catalysts prepared on alpha-alumina carriers made using a fluorine-containing substance as a fluxing agent. These carriers contain residual fluoride anion. The catalysts contain sulfate anion and at least one oxyanion of an element of groups 3b to 7b of the Periodic Table.
U.S. Pat. No. 4,874,739 also discloses the use of a fluorine-containing substance in preparing support for ethylene oxide catalysts. Examples 1 and 2 of that patent disclose admixing stannosulfate and cesium fluoride with aluminum oxide and then calcining an extrudate of this mixture to form an alpha-alumina support for catalysts prepared from silver oxalate, cesium hydroxide, ammonium perrhenate and ammonium sulfate. U.S. Pat. No. 4,829,044 discloses in the example a support prepared by mixing cesium fluoride with alumina and then calcining the alumina. The resultant alpha-alumina is used to prepare a catalyst from silver oxalate, cesium hydroxide, ammonium perrhenate and ammonium sulfate. See also U.S. Pat. Nos. 4,701,437; 4,783,437; and 4,806,519.
British Patent Specification 590,479 discloses ethylene oxide catalysts using a silicon support. The patent indicates that the activity of the catalysts may be promoted or modified by elements or compounds which are known to promote or modify the catalytic activity of silver metal such as gold, copper, platinum, nickel, and iron; the metal oxides and other metal compounds, particularly the alkali metal and alkaline earth metal oxides, hydroxides and carbonates; and some halogen compounds. At page 4, line 73 et seq., the patent discloses that a preliminary treatment of the silicon support material with a dilute hydrofluoric acid solution usually provides a more active catalyst.
U.S. Pat. No. 4,414,135 pertains to silver-based catalysts containing bromine and/or fluorine as an anionic component for the production of ethylene oxide. The patentees state at column 1, lines 30 to 36:
U.S. Pat. No. 4,123,385 discloses a silver ethylene oxide catalyst containing cesium and rubidium and states at column 2, line 61, et seq:
U.S. Pat. No. 4,419,276 discloses ethylene oxide catalysts containing various cation promoters, e.g., alkali metal promoters. The patent states at column 8, lines 32 et seq:
A similar disclosure is found in U.S. Pat. No. 4,455,392 at column 8, lines 36 et seq., and in U.S. Pat. No. 4,916,243 at column 16, lines 48 et seq.
U.S. Pat. No. 4,808,738 discloses ethylene oxide catalysts containing silver, a promoting amount of alkali metal, a promoting amount of rhenium and a promoting amount of rhenium co-promoter selected from sulfur, molybdenum, tungsten, chromium and mixtures thereof on a porous refractory support. At column 11, lines 23 et seq., the patent speculates that these co-promoters, which are preferably anions such as sulfate, molybdate, tungstate and chromates, can be prepared by the reactive dissolution of various non-anionic materials such as the oxides as well as other materials such as halides, oxyhalides, hydroxyhalides, hydroxides, sulfides, etc., of the metals. At column 14, lines 15 et seq., the patent states:
See also, U.S. Pat. Nos. 4,766,105; 4,820,675 and 4,833,261.
U.S. Pat. Nos. 2,671,764 and 4,248,740 disclose the presence of sulfate in silver catalysts for the epoxidation of ethylene.